Groups of 4 rhesus monkeys were immunized with two 2xlO 8 pfu doses of either a TK- deletion mutant of vaccinia virus, or recombinant vaccinia viruses containing the HIV-IIIB or HIV-RF envelope gene sequences in order to study HIV-1-vaccine-induced specific antibody responses in a subhuman primate species. Two animals in each group were then immunized with two 50 micro-g doses of a recombinant gpl6O vaccine to evaluate the immunogenicity of that antigen. Serological evaluations including western blotting, whole virus and recombinant ELISA assays, (51)Cr release antibodydependent cellular cytotoxicity assays, and HIV-1 neutralization assays were performed over a >1 year follow-up period. Both HIV-recombinant vaccines induced short-lived immunity to HIV-1 gpl6O following two immunizations. Following a first rgpl6O booster dose, antibody titers and antibody kinetics were similar to those observed with primary immunization, but the quality of the response appeared to differ in that some sera now possessed some low-titer neutralizing activity. Boosting with two doses of rgpl6O vaccine gave rise to more sustained titers elevations, and persistence of neutralizing responses in some animals. One of two animals receiving only rgpl6O seroconverted, but sera was non-neutralizing. These animals continue to be monitored serologically. An additional experiment evaluating varying doses of the two immunogens studied here is in progress in an additional group of rhesus monkeys.